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If you have serious health problems because of your weight and dieting hasn't worked for you, prescription weight-loss drugs may be an option. You should know, though, that prescription weight-loss drugs don't replace the need to make healthy changes in your eating habits and activity level.

Who is a candidate for weight-loss drugs?

Prescription weight-loss drugs are generally reserved for people who haven't been able to lose weight through diet and exercise, and who have health problems because of their weight. They're not for people who want to lose just a few pounds for cosmetic reasons.

Your doctor may consider weight-loss drugs for you if haven't been able to lose weight through diet and exercise and you meet one of the following:

Your body mass index (BMI) is greater than 30

Your BMI is greater than 27 and you have a serious medical problem related to obesity, such as diabetes or high blood pressure

Before selecting a medication for you, your doctor will consider your health history, possible side effects and potential interaction of weight-loss drugs with other medications you're taking.

How well do weight-loss drugs work?

When combined with a low-calorie diet and regular exercise, weight-loss drugs produce an average weight loss of 5 to 10 percent of total body weight within a year, which is a typical weight-loss goal. Diet and exercise are responsible for part of this weight loss, and medications are responsible for part as well.

Losing 5 to 10 percent of your total weight may not seem like much, but even modest weight loss can improve your health by:

Decreasing blood pressure

Decreasing lipid levels

Decreasing blood glucose levels

Increasing insulin sensitivity

It's important to keep in mind, however, that these medications may not work for everyone. And when you stop taking these medications, you're likely to regain much or all of the weight you lost.

Common weight-loss drugs

Diethylpropion (Tenuate) and phentermine (Adipex) are approved by the Food and Drug Administration (FDA) for only short-term use -- generally less than 12 weeks. Orlistat (Xenical), lorcaserin (Belviq) and a combination drug (Qsymia) are approved by the FDA for long-term use. Qsymia contains phentermine and an extended-release (ER) form of topiramate. Orlistat is also available in a reduced-strength form without a prescription (Alli).

Safety of weight-loss drugs

Diethylpropion (Tenuate), phentermine (Adipex), benzphetamine (Didrex) and phendimetrazine (Bontril) are approved for only short-term use -- generally less than 12 weeks. These drugs are classified as controlled substances because they have the potential to be abused. Because of possible side effects, these drugs aren't recommended if you have heart disease, high blood pressure or hyperthyroidism.

Orlistat (Xenical), lorcaserin (Belviq) and phentermine-topiramate (Qsymia) are approved for long-term use. Orlistat is also available in a reduced-strength form without a prescription (Alli).

After orlistat was approved, rare cases of serious liver injury were reported in some people taking it. No cause and effect relationship was established between. However, Xenical and Alli labels now advise people taking orlistat to be alert to signs and symptoms that could indicate liver injury, such as itching, loss of appetite, yellow eyes or skin, light-colored stool, or brown urine.

Belviq initially raised concerns because it works somewhat like fenfluramine -- which was withdrawn from the market because it damaged heart valves. However, there is no evidence that Belviq damages heart valves. Belviq may increase heart rate, so people taking it may need their heart rate checked.

Qsymia increases the risk of birth defects. Thus, the FDA required the manufacturer to have a risk evaluation and mitigation strategy (REMS). The REMS is intended to alert women to the risks and explain the need to avoid becoming pregnant while taking Qsymia. In addition, Qsymia is considered a controlled substance because one of its ingredients -- phentermine -- has the potential for abuse.

Factors to consider

If you meet the criteria for prescription weight-loss drugs, you and your doctor will need to evaluate the potential benefits against the possible risks of taking the medicine. Cost also is a consideration. Not all health insurance plans cover prescription weight-loss drugs.

As you consider weight-loss drugs, make sure that you make every effort to exercise, change your eating habits and adjust any other lifestyle factors that have contributed to your excess weight.

Weight-loss drugs aren't the easy answer to weight loss, but they can be a useful tool to help you make the necessary diet and lifestyle changes. Keeping off the pounds you've lost, however, is an ongoing concern. And many people, despite their efforts, still regain the weight.